One-Minute NGA Analysis Based on a Backflush-to-Detector Channel

Significance of the Topic

Natural gas composition analysis is critical for energy quality control, safety compliance, and calorific value determination.
Rapid and accurate measurement of light and heavy hydrocarbons supports real-time monitoring in industrial and field settings.

Objectives and Study Overview

This study presents a novel one-minute natural gas analysis (NGA) method using the Agilent 490 micro GC platform.
A backflush-to-detector channel is coupled with an existing Hayesep channel to expedite total analysis time below 60 seconds.

Methodology and Instrumentation

• Instrument: Agilent 490 micro GC configured with:
• Channel 1 (HSA): 40 cm straight Hayesep column for separation of N₂, CH₄, CO₂, and C₂H₆.
• Channel 2 (BF2D): 8 m CP-Sil 5CB with backflush-to-detector to capture C₆/C₆⁺ and C₃–C₅ hydrocarbons as a single peak.
• Carrier gas: Helium; injector temperature: 110 °C; injection time: 40 ms.
• Column temperatures: 80 °C (Hayesep), 72 °C (5CB); column head pressures: 280 kPa and 150 kPa respectively.

Main Results and Discussion

The combined configuration achieves full separation of air, C₁–C₂ and C₃–C₅ hydrocarbons with C₆/C₆⁺ eluted as one peak within 60 s.
Repeatability tests (n=15) yielded retention time RSD of 0.03–0.1 % and peak area RSD around 0.06–0.14 %.
Quantitation compared to the standard extended method showed differences below 0.34 % for C₆/C₆⁺ and below 0.03 % for other components.
Calculated calorific values and Wobbe Index from both methods were effectively identical, validating analytical accuracy.

Benefits and Practical Applications

• Reduction of analysis time by ≈60 % enables near real-time monitoring of natural gas streams.
• Single combined peak for C₆/C₆⁺ simplifies quantification when detailed speciation is not required.
• High precision and speed make the method ideal for field portables and tight process control.

Future Trends and Potential Applications

• Integration with automated sampling systems for continuous on-line monitoring.
• Extension of backflush timing optimization to other volatile and semi-volatile analytes.
• Application of advanced data processing and AI-based method development for further throughput gains.
• Development of multi-channel detectors combining flame ionization and mass spectrometry for enhanced specificity.

Conclusion

The new backflush-to-detector configuration on the Agilent 490 micro GC enables comprehensive NGA in under one minute with high precision.
This approach balances speed and accuracy, offering a robust solution for industrial, environmental, and field applications.

References

• Fast analysis of natural gas using the Agilent 490 micro GC natural gas analyzer, publication number 5991-0257.